Trans-impedance amplifier for ultrasound device and related apparatus and methods

ABSTRACT

A variable current trans-impedance amplifier (TIA) for an ultrasound device is described. The TIA may be coupled to an ultrasonic transducer to amplify an output signal of the ultrasonic transducer representing an ultrasound signal received by the ultrasonic transducer. During acquisition of the ultrasound signal by the ultrasonic transducer, one or more current sources in the TIA may be varied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation, claiming the benefit under 35 U.S.C.§ 120, of U.S. patent application Ser. No. 14/957,395, filed Dec. 2,2015, under Attorney Docket No. B1348.70023US00 and entitled“TRANS-IMPEDANCE AMPLIFIER FOR ULTRASOUND DEVICE AND RELATED APPARATUSAND METHODS,” which is hereby incorporated herein by reference in itsentirety.

BACKGROUND Field

The present application relates to ultrasound devices having anamplifier for amplifying received ultrasound signals.

Related Art

Ultrasound probes often include one or more ultrasound sensors whichsense ultrasound signals and produce corresponding electrical signals.The electrical signals are processed in the analog or digital domain.Sometimes, ultrasound images are generated from the processed electricalsignals.

BRIEF SUMMARY

According to an aspect of the present application, an ultrasoundapparatus is provided, comprising an ultrasound sensor and a variablecurrent trans-impedance amplifier (TIA). The variable current TIA iscoupled to the ultrasound sensor and configured to receive and amplifyan output signal from the ultrasound sensor. The variable current TIAhas a variable current source.

According to an aspect of the present application, a method is provided,comprising acquiring an ultrasound signal with an ultrasound sensorduring an acquisition period and outputting, from the ultrasound sensor,an analog electrical signal representing the ultrasound signal. Themethod further comprises amplifying the electrical signal with avariable current trans-impedance amplifier (TIA), including varying acurrent of the variable current TIA during the acquisition period.

According to an aspect of the present application, a method is provided,comprising acquiring an ultrasound signal with an ultrasound sensorduring an acquisition period and outputting, from the ultrasound sensor,an analog electrical signal representing the ultrasound signal. Themethod further comprises amplifying the electrical signal with avariable current trans-impedance amplifier (TIA), including decreasing anoise floor of the variable current TIA during the acquisition period.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments of the application will be describedwith reference to the following figures. It should be appreciated thatthe figures are not necessarily drawn to scale. Items appearing inmultiple figures are indicated by the same reference number in all thefigures in which they appear.

FIG. 1 is a block diagram of an ultrasound device including an amplifierfor amplifying an ultrasound signal, according to a non-limitingembodiment of the present application.

FIG. 2 illustrates the amplifier of FIG. 1 in greater detail, coupled tothe ultrasonic transducer and averaging circuit of FIG. 1, according toa non-limiting embodiment of the present application.

FIG. 3A is a circuit diagram illustrating an implementation of theamplifier of FIG. 2, according to a non-limiting embodiment of thepresent application.

FIG. 3B is a circuit diagram of an implementation of one variableimpedance circuit of FIG. 3A, according to a non-limiting embodiment ofthe present application.

FIG. 3C is a circuit diagram of an implementation of another variableimpedance circuit of FIG. 3A, according to a non-limiting embodiment ofthe present application

FIG. 4 is a graph illustrating the behavior of two variable currentsources of an amplifier during an acquisition period, as may beimplemented by the amplifier of FIGS. 2 and 3A, according to anon-limiting embodiment of the present application.

FIG. 5 is a graph illustrating an electrical signal representing anultrasound signal, and a noise floor of an amplifier during anacquisition period, according to a non-limiting embodiment of thepresent application.

DETAILED DESCRIPTION

Aspects of the present application relate to amplification circuitry foran ultrasound device. An ultrasound device may include one or moreultrasonic transducers configured to receive ultrasound signals andproduce electrical output signals. Thus, the ultrasonic transducers maybe operated as ultrasound sensors. The ultrasound device may include oneor more amplifiers for amplifying the electrical output signals. Thepower consumed by, the noise generated by, and the linear signalamplification quality provided by, the amplifier may depend on an amountof current consumed by the amplifier. In some embodiments, the amplifierhas a variable current source. The variable current source is adjustedduring acquisition of an ultrasound signal to maintain the noise levelof the amplifier below the signal level and to maintain linearamplification, while at the same time reducing the amount of powerconsumed by the amplifier. In some embodiments, the amplifier is a TIA.

The aspects and embodiments described above, as well as additionalaspects and embodiments, are described further below. These aspectsand/or embodiments may be used individually, all together, or in anycombination of two or more, as the application is not limited in thisrespect.

FIG. 1 illustrates a circuit for processing received ultrasound signals,according to a non-limiting embodiment of the present application. Thecircuit 100 includes N ultrasonic transducers 102 a . . . 102 n, whereinN is an integer. The ultrasonic transducers are sensors in someembodiments, producing electrical signals representing receivedultrasound signals. The ultrasonic transducers may also transmitultrasound signals in some embodiments. The ultrasonic transducers maybe capacitive micromachined ultrasonic transducers (CMUTs) in someembodiments. The ultrasonic transducers may be piezoelectricmicromachined ultrasonic transducers (PMUTs) in some embodiments.Further alternative types of ultrasonic transducers may be used in otherembodiments.

The circuit 100 further comprises N circuitry channels 104 a . . . 104n. The circuitry channels may correspond to a respective ultrasonictransducer 102 a . . . 102 n. For example, there may be eight ultrasonictransducers 102 a . . . 102 n and eight corresponding circuitry channels104 a . . . 104 n. In some embodiments, the number of ultrasonictransducers 102 a . . . 102 n may be greater than the number ofcircuitry channels.

The circuitry channels 104 a . . . 104 n may include transmit circuitry,receive circuitry, or both. The transmit circuitry may include transmitdecoders 106 a . . . 106 n coupled to respective pulsers 108 a . . . 108n. The pulsers 108 a . . . 108 n may control the respective ultrasonictransducers 102 a . . . 102 n to emit ultrasound signals.

The receive circuitry of the circuitry channels 104 a . . . 104 n mayreceive the electrical signals output from respective ultrasonictransducers 102 a . . . 102 n. In the illustrated example, eachcircuitry channel 104 a . . . 104 n includes a respective receive switch110 a . . . 110 n and an amplifier 112 a . . . 112 n. The receiveswitches 110 a . . . 110 n may be controlled to activate/deactivatereadout of an electrical signal from a given ultrasonic transducer 102 a. . . 102 n. More generally, the receive switches 110 a . . . 110 n maybe receive circuits, since alternatives to a switch may be employed toperform the same function. The amplifiers 112 a . . . 112 n, as well asamplifier 300 of FIG. 3 (described below), may be TIAs in someembodiments. One or more of the amplifiers 112 a . . . 112 n may bevariable current amplifiers. As will be described further below, thecurrent of the amplifiers may be varied during an acquisition period,thus adjusting the power consumption, noise level, and linearity of theamplifiers. The amplifiers 112 a . . . 112 n may output analog signals.

The circuit 100 further comprises an averaging circuit 114, which isalso referred to herein as a summer or a summing amplifier. In someembodiments, the averaging circuit 114 is a buffer or an amplifier. Theaveraging circuit 114 may receive output signals from one or more of theamplifiers 112 a . . . 112 n and may provide an averaged output signal.The averaged output signal may be formed in part by adding orsubtracting the signals from the various amplifiers 112 a . . . 112 n.The averaging circuit 114 may include a variable feedback resistance.The value of the variable feedback resistance may be adjusteddynamically based upon the number of amplifiers 112 a . . . 112 n fromwhich the averaging circuit receives signals. In some embodiments, thevariable resistance may include N resistance settings. That is, thevariable resistance may have a number of resistance settingscorresponding to the number of circuitry channels 104 a . . . 104 n.Thus, the average output signal may also be formed in part byapplication of the selected resistance to the combined signal receivedat the inputs of the averaging circuit 114.

The averaging circuit 114 is coupled to an auto-zero block 116. Theauto-zero block 116 is coupled to a programmable gain amplifier 118which includes an attenuator 120 and a fixed gain amplifier 122. Theprogrammable gain amplifier 118 is coupled to an ADC 126 via ADC drivers124. In the illustrated example, the ADC drivers 124 include a first ADCdriver 125 a and a second ADC driver 125 b. The ADC 126 digitizes thesignal(s) from the averaging circuit 114.

While FIG. 1 illustrates a number of components as part of a circuit ofan ultrasound device, it should be appreciated that the various aspectsdescribed herein are not limited to the exact components orconfiguration of components illustrated. For example, aspects of thepresent application relate to the amplifiers 112 a . . . 112 n, and thecomponents illustrated downstream of those amplifiers in circuit 100 areoptional in some embodiments.

The components of FIG. 1 may be located on a single substrate or ondifferent substrates. For example, as illustrated, the ultrasonictransducers 102 a . . . 102 n may be on a first substrate 128 a and theremaining illustrated components may be on a second substrate 128 b. Thefirst and/or second substrates may be semiconductor substrates, such assilicon substrates. In an alternative embodiment, the components of FIG.1 may be on a single substrate. For example, the ultrasonic transducers102 a . . . 102 n and the illustrated circuitry may be monolithicallyintegrated on the same semiconductor die. Such integration may befacilitated by using CMUTs as the ultrasonic transducers.

According to an embodiment, the components of FIG. 1 form part of anultrasound probe. The ultrasound probe may be handheld. In someembodiments, the components of FIG. 1 form part of an ultrasound patchconfigured to be worn by a patient.

FIG. 2 illustrates a non-limiting example of the amplifier 112 a of FIG.1 in greater detail. The same configuration may be used for the otheramplifiers 112 n of FIG. 1. For context, the ultrasonic transducer 102 aand averaging circuit 114 are also illustrated, while for simplicity thereceive switch 110 a is omitted.

In this non-limiting embodiment, the amplifier 112 a is implemented as atwo-stage operational amplifier (“op-amp” for short). The first stage202 is coupled to the ultrasonic transducer 102 a. The second stage 204is coupled between the first stage 202 and the averaging circuit 114.The second stage 204 provides the output signal of the amplifier 112 a,in this non-limiting example.

The first stage 202 and second stage 204 each have a variable currentsource. The variable current source 203 is provided for the first stage202 and sinks a current I1. The variable current source 205 is providedfor the second stage 204 and sinks a current I2. Although the variablecurrent sources 203 and 205 are illustrated as distinct from therespective stages 202 and 204, they may be considered part of therespective stages.

With a two-stage amplifier construction as shown in FIG. 2, the noiseand linearity of the amplified signal may be controlled independently.The noise of the amplifier 112 a is impacted primarily by the firststage 202. The linearity of the amplifier 112 a is impacted primarily bythe second stage 204. More generally, the same may be true for amulti-stage amplifier having two or more stages, such that the noise ofthe amplifier is impacted primarily by the first stage and the linearityof the amplifier is impacted primarily by the last stage. Applicant hasappreciated that during acquisition of an ultrasound signal, referred toherein as an acquisition period, the noise and linearity of theamplified signal may vary in importance. When the ultrasound signal isinitially received, early in the acquisition period and corresponding toshallow depths when the ultrasound signal is a reflected signal, theassociated noise will be relatively low compared to the received signalamplitude, but the linearity of the amplified signal may be ofrelatively high importance. However, later during the acquisitionperiod, corresponding to greater depths when the ultrasound signal is areflected signal, the ultrasound signal is likely to become smaller, andthus the noise of the signal is of increased importance. Thus, theamplifier 112 a of FIG. 2 is designed to allow for independent andvariable control of noise and linearity. The control may be provided viathe variable current sources 203 and 205.

Early during an acquisition period, the variable current source 203 maybe controlled to sink a relatively small amount of current, while thecurrent source 205 may be controlled to sink a relatively large amountof current. In such a scenario, the second stage 204 may operate tocontrol the linearity of the amplified signal produced by the amplifier112 a, while the first stage 202 may control the noise of the amplifiedsignal 202 to a lesser extent than that to which it is capable. Later inthe acquisition period, the current sunk by the variable current source203 may be increased while the current sunk by the variable currentsource 205 may be decreased. As the current sunk by the variable currentsource 203 is increased, the first stage 202 may operate to control thenoise of the amplifier 112 a to a greater extent. As the current sunk bythe variable current source 205 is decreased, the second stage 204 mayoperate to control the linearity of the amplifier 112 a to a lesserextent. Thus, dynamic current biasing of the amplifier 112 a, and firststage 202 and second stage 204 more specifically, may be implemented tocontrol the power, noise, and linearity characteristics of the amplifierduring an acquisition period.

The dynamic control of current sources 203 and 205 may be achieved usinga digital controller, an example being shown in FIG. 3A. The variablecurrent sources 203 and 205 may each include two or more programmablecurrent settings. The greater the number of settings, the greater thecontrol over the current sunk by the current sources 203 and 205.

The amplifier 112 a also includes a variable feedback impedance 206. Insome embodiments, the variable feedback impedance is a variable RCfeedback circuit. An example of the variable RC feedback circuit isillustrated in FIG. 3A and described in connection with that figure. Thefeedback impedance determines the transimpedance gain of thetransimpedance amplifier, such that the input current signal may beconverted into an output voltage of varying amplitude.

It should be appreciated from FIG. 2 and the foregoing description thatan embodiment of the application provides a multi-stage TIA having twoor more independently controllable variable current sources, with avariable feedback impedance. The variable current sources may allow fordynamic current biasing of the TIA, for example during an acquisitionperiod. Thus, the power consumption, noise, and linearity of theamplifier may be adjusted during the acquisition period.

FIG. 3A is a circuit diagram illustrating an implementation of theamplifier 112 a of FIG. 2, according to a non-limiting embodiment of thepresent application. The amplifier 300 has an input 302 and an output304. The input 302 may be coupled to an ultrasonic transducer or areceive switch, as described previously in connection with FIGS. 1 and2, and may receive an electrical signal representing an ultrasoundsignal received by the ultrasonic transducer. The output 304 may providean amplified output signal of the amplifier 112 a, and may be coupled toan averaging circuit or other component to which it is desired toprovide the amplified output signal.

The amplifier 300 includes a first stage 306 and a second stage 308,which may be implementations of the first stage 202 and second stage 204of FIG. 2, respectively. The first stage 306 includes an NMOS transistor310 having a gate configured to receive the signal at input 302. PMOStransistor 312 and PMOS transistor 314 have their gates coupled, withthe drain of PMOS transistor 312 coupled to the drain of NMOS transistor310. The gate of transistor 312 is coupled to its drain. Transistors 312and 314 are also configured to receive a power supply voltage VDDA. Thefirst stage 306 further comprises NMOS transistor 316 having a gateconfigured to receive a bias voltage provided by an RC circuit. The RCcircuit includes two resistors, of value R, with a capacitor C_(b)coupled in parallel with one of the resistors. The other resistorreceives the power supply voltage VDDA. The drain of PMOS transistor 314is coupled to the drain of NMOS transistor 316. An example value for Ris 50 kOhm and an example value for C_(b) is 10 pF, althoughalternatives for both are possible, such as +/−20% of those valueslisted, or any value or range of values within such ranges.

The second stage 308 includes a PMOS transistor 318 configured toreceive the output of the first stage 306. In particular, the gate ofPMOS transistor 318 is coupled to a node between transistors 314 and 316of the first stage 306. The source of PMOS transistor 318 receives VDDA.A variable impedance circuit 320 is also provided in the second stage308. The variable impedance circuit 320 includes a variable capacitorC_(C) in series with a variable resistor R_(Z), and thus is a variableRC circuit in this embodiment. Variable impedance circuit 320 mayprovide stable operation of the amplifier 300 when the gain of theamplifier, or the currents of the currents sources, are varied. Thus,the variable impedance circuit may be provided to maintain stableoperation of the amplifier 300 for all the current magnitudes sunk bythe variable current sources 321 and 325. That is, the values of C_(C)and R_(Z) may be adjusted during operation of the amplifier 300 toaccount for the different current settings programmed by the digitalcontroller 330

A variable current source is provided for each of the stages 306 and308. The variable current source 321 for the first stage 306 includesthree parallel connected current sources 322 a, 322 b, and 322 c.Current source 322 a sinks a current I_(A), current source 322 b sinks acurrent 2I_(A), and current source 322 c sinks a current 4I_(A). Thecurrent sources 322 a-322 c are coupled to the first stage 306 byrespective switches 324 a, 324 b, and 324 c, which effectively provides3 bits (8 states) of control of the current. The current I_(A) may equal100 microAmps or +/−20% of that value, or any value or range of valueswithin such ranges, as examples.

The variable current source 325 for the second stage 308 includes threeparallel connected current sources 326 a, 326 b, and 326 c. Currentsource 326 a sinks a current I_(B), current source 326 b sinks a current2I_(B), and current source 326 c sinks a current 4I_(B). The currentsources 326 a-326 c are coupled to the second stage 308 by respectiveswitches 328 a, 328 b, and 328 c, which effectively provides 3 bits (8states) of control of the current. The current I_(B) may equal 50microAmps or +/−20% of that value, or any value or range of valueswithin such ranges, as examples.

While FIG. 3A illustrates variable current sources each include threeparallel-coupled current sources, it should be appreciated that not allaspects of the present application are limited in this manner. That is,variable current sources may be implemented in various manners,including alternative manners to those illustrated. For example, more orfewer than three current sources may be coupled in parallel to create avariable current source. Also, the magnitudes of the current sources maybe different than those illustrated in FIG. 3A. Any suitable magnitudesmay be provided to allow for operation over a desired range of currents.

A digital controller 330 is provided to control operation of thevariable current sources 321 and 325. The digital controller providescontrol signals to (digitally) program the currents of the variablecurrent sources. In the illustrated example, the digital controller 330provides one or more switching signals S1 to control operation of theswitches 324 a-324 c, and one or more switching signals S2 to controloperation of the switches 328 a-328 c. In this manner, the amount ofcurrent sunk by the variable current sources may be varied independentlyduring operation of the amplifier 300, for example during an acquisitionperiod. According to a non-limiting example, the digital controller 330decreases the current sunk by variable current source 325 during theacquisition period and increases the current sunk by variable currentsource 321 during the acquisition period through suitable operation ofthe switching signals S1 and S2.

The digital controller 330 may be any suitable type of controller. Thedigital controller may include integrated circuitry. In someembodiments, the digital controller 330 may include or be part of anapplication specific integrated circuit (ASIC). In some embodiments, thedigital controller 330 may not be specific to the amplifier 300. Forexample, a digital controller may be provided to control more than onecomponent of the circuit of FIG. 1, one of which may be the amplifiers112 a . . . 112 n.

The amplifier 300 further includes a variable feedback impedance 332formed by variable capacitor C_(f) and variable resistor R_(f). Thecapacitor C_(f) and resistor R_(f) may be coupled between the output 304and the input 302, and may be in parallel with each other. The variablefeedback impedance 332 may control the gain of the amplifier 300. Thus,the values of C_(f) and R_(f) may be adjusted to vary the amplifier'sgain.

The variable feedback impedance 332 and the variable impedance circuit320 may be controlled in any suitable manner. In one embodiment, thedigital controller 330 may set the values of the feedback impedances.However, alternatives manners of control may be used.

It should be appreciated that the described groupings of components inconnection with FIG. 3A are not limiting. For example, while certaincomponents illustrated in that figure are described as being part of afirst stage or a second stage, the identification of the first andsecond stages is not limiting. The first and second stages may includemore, fewer, or different components than those illustrated.

FIG. 3B is a circuit diagram of an implementation of the variableimpedance circuit 320 of FIG. 3A, according to a non-limiting embodimentof the present application. The variable impedance circuit 320 includesa number of switches 340 a . . . 340 n configured in parallel andconfigured to receive respective control signals SWa . . . SWn. In someembodiments, the digital controller 330 may provide the control signalsSWa . . . SWn, although alternatives may be used. Each switch is coupledin series with a respective capacitor C_(C) and resistor R_(Z). Theimpedance of the variable impedance circuit 320 may be adjusted duringan acquisition period through suitable provision of the control signalsSWa . . . SWn. Any suitable number of parallel signal paths may beprovided, so that the illustrated example of two parallel signal pathsis non-limiting. The number of parallel signal paths and the capacitanceand resistive values provided may be selected to provide sufficientcontrol of the feedback impedance to account for the variable operationof the amplifier across the range of operating scenarios resulting fromthe variation of the variable current sources. For example, for a givenamplifier gain dictated by variable feedback impedance 332, appropriatesettings of variable impedance circuit 320 may be selected. In someembodiments, a lookup table may be utilized to determine the appropriatesettings of variable impedance circuit 320 based on a given gain set byvariable feedback impedance 332.

In both FIGS. 3A and 3B, the values of C_(C) and R_(Z) may be selectedto provide desired operating characteristics. As examples, R_(Z) may beequal to 3 kOhms in some embodiments, and C_(C) may be equal to 300 fF.Alternatives for both are possible. For example, they may assume valueswithin +/−20% of those values listed, or any value or range of valueswithin such ranges.

FIG. 3C is a circuit diagram of an implementation of the variableimpedance circuit 332 of FIG. 3A, according to a non-limiting embodimentof the present application. The variable impedance circuit 332 includesa number of complementary switches 350 a, 350 b . . . 350 n. Each switchreceives respective control signals SLa, SLb . . . SLn and SHa, SHb . .. SHn. The control signals may be provided by the digital controller 330in some embodiments, although alternatives may be used. Thecomplementary switches are coupled to respective parallel-connected RCcircuits C_(f), R_(f). While three complementary switches are shown inFIG. 3C, any suitable number may be provided to allow for sufficientcontrol of the gain of the amplifier 300.

In both FIGS. 3A and 3C, the values of C_(f) and R_(f) may be selectedto provide desired operating characteristics. As examples, R_(f) may beequal to 180 kOhms in some embodiments, and C_(f) may be equal to 84 fF.Alternatives for both are possible. For example, they may assume valueswithin +/−20% of those values listed, or any value or range of valueswithin such ranges.

FIG. 4 is a graph illustrating the behavior of two variable currentsources of a variable current amplifier during an acquisition period, asmay be implemented by the amplifier of FIGS. 2 and 3A, which again maybe a TIA. For example, the illustrated behavior may be implemented bythe variable current sources 203 and 205 of FIG. 2. The x-axisrepresents time during an acquisition period, ranging from t0 to t8. They-axis represents the current of the current source, having valuesranging from I0 to I8. The values of t0-t8 and I0-I8 may be any suitablevalues for operation of a given ultrasound system, as the variousaspects described herein are not limited to implementation of anyspecific time or current values. Also, the number of time intervalsduring an acquisition period is non-limiting, as more or fewer may beimplemented. The number of current values which may be implemented isnon-limiting, as more or fewer may be implemented.

Curve 402 represents the current of a variable current source of asecond stage of a variable current amplifier. Thus, curve 402 mayrepresent the current of current source 205 of FIG. 2. Curve 404represents the current of a variable current source of a first stage ofthe variable current amplifier. Thus, curve 404 may represent thecurrent of current source 203 of FIG. 2.

FIG. 4 illustrates that the currents of the first and second stages ofthe variable current amplifier move in opposing directions during theacquisition period. That is, curve 402 decreases moving from time t0 totime t8, while curve 404 increases during the same time. As previouslydescribed in connection with FIG. 2, the first and second stages of thevariable current amplifier may impact different characteristics of thevariable current amplifier behavior, such as noise and linearity. Thus,when operating in the manner illustrated in FIG. 4, the impact of thetwo stages of the variable current amplifier may vary during theacquisition period. That is, the impact of the second stage may begreater initially, up to time t4, while the impact of the first stagemay be greater thereafter, from time t4 to time t8.

As previously described in connection with FIG. 3A, the currents of thetwo stages of a two-stage op-amp being used to implement a variablecurrent amplifier may be controlled by digital codes. Thus, the currentvalues I0-I7 of FIG. 4 may correspond to different digital codes set bya digital controller, such as digital controller 330 of FIG. 3A.

While FIG. 4 illustrates that the currents in the first and secondstages of the amplifier switch at the same times, not all embodimentsare limited in this respect. For example, the current in the secondstage could be adjusted at times offset from those at which the currentin the first stage is adjusted. Likewise, the currents of the two stagesneed not be adjusted the same number of times during an acquisitionperiod.

As described previously, an aspect of the present application providesan amplifier with a variable current source which is controlled toadjust the noise of the amplifier during an acquisition period. FIG. 5illustrates an example of such operation.

In FIG. 5, the voltage of an electrical signal 502 output by anultrasonic transducer, and thus representing a detected ultrasoundsignal, is illustrated as a function of time. Dashed line 504 representsthe noise floor of an amplifier used to amplify the electrical signal502, and may correspond to the noise floor of an amplifier of the typesdescribed herein, such as amplifier 112 a. It can be seen that duringthe acquisition period, the magnitude of the electrical signaldecreases. Likewise, the noise floor of the amplifier is decreased. Sucha decrease in the noise floor may be achieved by controlling the currentsunk by a variable current source of the amplifier in the mannerdescribed previously herein. For example, referring to FIG. 2, thevariable current source 203 may be increased during the acquisitionperiod to decrease the noise floor of the amplifier 112 a. The noisefloor may be adjusted to a level which provides an acceptablesignal-to-noise ratio (SNR).

FIG. 5 also illustrates a constant noise floor 506. It can be seen thatwhile the constant noise floor 506 is at the same level as dashed line504 toward the end of the acquisition period, the constant noise floor506 is lower than the value of the dashed line 504 up to that point. Ashas been described herein, the noise level of an amplifier may bedependent on the current consumed by the amplifier, and in suchsituations it should be appreciated that operating with a constant noisefloor 506 requires significantly more current (and therefore power) thanoperating according to dashed line 504. Thus, aspects of the presentapplication providing for a variable current amplifier to amplifyultrasound signals may provide substantial power savings compared toamplifiers operating with a constant noise level.

The amount of power savings may be significant. For example, in thecircuit 100, the amplifiers 112 a . . . 112 n may consume a significantamount of power. In some embodiments, the amplifiers 112 a . . . 112 nmay consume more power than any other components of the circuit 100.Accordingly, reducing the power consumption of the amplifiers 112 a . .. 112 n may provide a significant reduction in power of the circuit 100.In some embodiments, utilizing variable current amplifiers of the typesdescribed herein may provide up to a 25% power reduction, up to a 40%power reduction, up to a 50% power reduction, or any range or valuewithin such ranges, in terms of the operation of the amplifier. Theresulting power reduction for the circuit 100 may be up to 10%, up to20%, up to 25%, or any range or value within such ranges.

Having thus described several aspects and embodiments of the technologyof this application, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those of ordinaryskill in the art. Such alterations, modifications, and improvements areintended to be within the spirit and scope of the technology describedin the application. It is, therefore, to be understood that theforegoing embodiments are presented by way of example only and that,within the scope of the appended claims and equivalents thereto,inventive embodiments may be practiced otherwise than as specificallydescribed.

As an example, certain embodiments described herein have focused ontwo-stage amplifiers. However, the techniques described herein may applyto multi-stage amplifiers having two or more stages. When more than twostages are used, the first stage may predominantly control the noise ofthe amplifier, while the last stage may predominantly control thelinearity of the amplifier.

As described, some aspects may be embodied as one or more methods. Theacts performed as part of the method(s) may be ordered in any suitableway. Accordingly, embodiments may be constructed in which acts areperformed in an order different than illustrated, which may includeperforming some acts simultaneously, even though shown as sequentialacts in illustrative embodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements.

As used herein, the term “between” used in a numerical context is to beinclusive unless indicated otherwise. For example, “between A and B”includes A and B unless indicated otherwise.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively.

What is claimed is:
 1. An ultrasound apparatus, comprising: anultrasound sensor; and a variable current trans-impedance amplifier(TIA) coupled to the ultrasound sensor and configured to receive andamplify an output signal from the ultrasound sensor, the variablecurrent TIA being a multi-stage operational amplifier having a firststage and a last stage and including a first variable current sourcecoupled to the first stage and a second variable current source coupledto the last stage; wherein the first stage is arranged to receive theoutput signal from the ultrasound sensor and the last stage is arrangedto provide an output signal of the variable current TIA; and wherein thefirst variable current source comprises two or more current sourcesconnected in parallel, and at least one of the two or more currentsources is coupled to the first stage through a switch.
 2. Theultrasound apparatus of claim 1, wherein the first and second variablecurrent sources are independently controllable.
 3. The ultrasoundapparatus of claim 1, wherein the first and second variable currentsources are digitally programmable.
 4. The ultrasound apparatus of claim1, further comprising a control circuit coupled to the first variablecurrent source and the second variable current source and configured tocontrol a first amount of current through the first variable currentsource and a second amount of current through the second variablecurrent source.
 5. The ultrasound apparatus of claim 1, wherein theultrasound sensor and the variable current TIA are monolithicallyintegrated on a semiconductor chip.
 6. The ultrasound apparatus of claim1, wherein the first variable current source provides eight states for acurrent of the first variable current source.
 7. The ultrasoundapparatus of claim 1, wherein the first variable current sourcecomprises a first current source providing a first current, a secondcurrent source providing a second current, and a third current sourceproviding a third current, the first current being approximately half ofthe second current and approximately a quarter of the third current. 8.A method, comprising: acquiring an ultrasound signal with an ultrasoundsensor during an acquisition period and outputting, from the ultrasoundsensor, an analog electrical signal representing the ultrasound signal;and amplifying the analog electrical signal with a variable currenttrans-impedance amplifier (TIA), including varying a current of thevariable current TIA during the acquisition period; wherein: thevariable current TIA is a multi-stage operational amplifier having afirst stage and a last stage; varying the current of the variablecurrent TIA during the acquisition period includes independently varyinga current of the first stage and a current of the last stage; andindependently varying the current of the first stage and the current ofthe last stage comprises increasing the current of the first stage inintervals during the acquisition period and decreasing the current ofthe last stage in intervals during the acquisition period.
 9. The methodof claim 8, wherein amplifying the analog electrical signal with thevariable current trans-impedance amplifier (TIA) further comprisesdecreasing a noise floor of the variable current TIA during theacquisition period.
 10. The method of claim 8, further comprising:simultaneously increasing the current of the first stage and decreasingthe current of the last stage after a time interval.
 11. An ultrasoundapparatus, comprising: an ultrasound sensor configured to acquire anultrasound signal during an acquisition signal; and a variable currenttrans-impedance amplifier (TIA) coupled to the ultrasound sensor andconfigured to receive and amplify the ultrasound signal from theultrasound sensor, the variable current TIA being a multi-stageoperational amplifier having a first stage and a last stage andincluding a first variable current source coupled to the first stage anda second variable current source coupled to the last stage; and acontrol circuit coupled to the variable current TIA and configured toindependently vary a current of the first stage and a current of thelast stage during the acquisition period by increasing the current ofthe first stage in intervals during the acquisition period anddecreasing the current of the last stage in intervals during theacquisition period.
 12. The ultrasound apparatus of claim 11, whereinthe control circuit is configured, when independently varying thecurrent of the first stage and the current of the last stage, todigitally program the first and second variable current sources.
 13. Theultrasound apparatus of claim 11, wherein the variable current TIA isconfigured, when amplifying the ultrasound signal, to decrease a noisefloor of the variable current TIA during the acquisition period.
 14. Theultrasound apparatus of claim 11, wherein the ultrasound sensor and thevariable current TIA are monolithically integrated on a semiconductorchip.
 15. The ultrasound apparatus of claim 11, wherein the firstvariable current source provides eight states for a current of the firstvariable current source.
 16. The ultrasound apparatus of claim 11,wherein the first variable current source comprises a first currentsource providing a first current, a second current source providing asecond current, and a third current source providing a third current,the first current being approximately half of the second current andapproximately a quarter of the third current.
 17. An ultrasoundapparatus, comprising: an ultrasound sensor configured to acquire anultrasound signal during an acquisition signal; and a variable currenttrans-impedance amplifier (TIA) coupled to the ultrasound sensor andconfigured to receive and amplify the ultrasound signal from theultrasound sensor, the variable current TIA being a multi-stageoperational amplifier having a first stage and a last stage andincluding a first variable current source coupled to the first stage anda second variable current source coupled to the last stage; and acontrol circuit coupled to the variable current TIA and configured toindependently vary a current of the first stage and a current of thelast stage during the acquisition period by simultaneously increasingthe current of the first stage and decreasing the current of the laststage after a time interval.
 18. The ultrasound apparatus of claim 17,wherein the control circuit is configured, when independently varyingthe current of the first stage and the current of the last stage, todigitally program the first and second variable current sources.
 19. Theultrasound apparatus of claim 17, wherein the variable current TIA isconfigured, when amplifying the ultrasound signal, to decrease a noisefloor of the variable current TIA during the acquisition period.
 20. Theultrasound apparatus of claim 17, wherein the first variable currentsource provides eight states for a current of the first variable currentsource.